Soft tissue sarcomas arise in nearly 10,000 persons in the United States each year, and about 40% of patients die of either loco-regional disease or distant metastasis. As sarcomas and other solid tumors outgrow their blood supply, hypoxia (or oxygen deprivation) stabilizes hypoxia inducible factors 1a and 2a (HIFs), which bind to ARNT (a.k.a. HIF-) and drive the expression of over 150 genes. These genes regulate) a variety of tumor phenotypes including tumor angiogenesis (or new blood vessel formation), invasion, and metastasis. Vascular endothelial growth factor (VEGF) is one of the genes controlled by HIFs and is also one of the most important factors driving tumor angiogenesis. HIFs and VEGF are overexpressed in human sarcomas, and increasing levels of these factors correlate with extent of disease and metastasis. HIFs and VEGF may also contribute to tumor resistance to radiation therapy. Numerous preclinical studies have found that anti-VEGF therapies can augment the effects of radiation therapy, and this synergistic effect was confirmed in a phase II clinical trial of neoadjuvant bevacizumab (an anti-VEGF antibody) and radiation therapy for sarcomas. The long-term objective of this proposal is to expand the use of agents targeting VEGF and HIFs in patients with sarcoma to reduce loco-regional recurrence and distant metastasis. Consequently, this proposal is designed to test the hypothesis that HIFs and VEGF play critical and interdependent roles in regulating sarcoma progression, metastasis, and radiation sensitivity. To test this hypothesis, this research proposal will (1) determine the role of HIFs in sarcomagenesis and metastasis, (2) determine the effects of VEGF inhibition on HIF activity, tumor invasion, and metastasis, and (3) determine the effects of HIF and VEGF inhibition on response of sarcomas to radiation. The methods of this proposal include analysis of sarcoma cell lines and primary endothelial cells in vitro, analysis of genetically engineered mouse models, and analysis of tumor tissue samples from sarcoma patients.